The present invention relates to a device for transmitting and/or receiving electromagnetic waves, more especially to an antenna known as a xe2x80x9cprinted antennaxe2x80x9d.
In everything that follows, the term xe2x80x9cprinted antennaxe2x80x9d (or xe2x80x9cmicrostrip antennaxe2x80x9d) will refer to an antenna made using so-called xe2x80x9cmicrostripxe2x80x9d technology comprising a radiating element, typically a xe2x80x9cpatchxe2x80x9d, a slot, etc., or an array of such elements, the number of elements depending on the sought-after gain. This type of antenna is used in particular as primary source at the focus of a lens or of a parabola.
By virtue of their lightness, their flatness, the flexibility of design which they offer, their ease of incorporation into numerous items of electronic equipment, the compatibility of their manufacture with proven techniques for the mass production of printed circuits and finally their low cost price, printed antennas are becoming increasingly used in numerous wireless communications systems (local wireless networks, access networks whether they be terrestrial or satellite, etc.).
Now, in numerous applications, it may be advantageous and/or necessary to use circular polarization for the transmission/reception antennas.
However, printed antennas are better adapted to transmit/receive a linearly polarized wave.
Thus, to transmit/receive circular polarization with printed antennas, several techniques have been implemented. These techniques are described, for example, in xe2x80x9cHandbook of Microstrip Antennasxe2x80x9d edited by J R James and P S Hall; published by: Peter Peregrinus Ltd, London, United Kingdom-ISBN 0 86341 150 9. In particular, chapter 4: Circular polarisation and bandwith, pp. 219-274.
These techniques consist essentially in simultaneously exciting two linearly polarized waves 90xc2x0 out of phase. Therefore, the quality of the circular polarization which can be quantified by the ellipticity ratio (or xe2x80x9caxial ratioxe2x80x9d) of the wave radiated or received by the antenna can only be obtained over a narrow frequency band.
Solutions for widening the frequency band such as the use of a hybrid coupler associated with a radiating element or the use of the technique of sequential rotation in the case of an array (see xe2x80x9capplication of sequential feeding to wide bandwith, circularly polarised microstrip patch arraysxe2x80x9d P. S. Hall, IEE Proceedings, Vol. 136, Pt. H, No 5, October 1989) make it possible to widen this frequency band.
However, it is not always possible to implement these solutions.
Moreover:
for certain applications, the bandwidths obtained with these techniques remain inadequate,
in the case of the use of sequential rotation, the quality of the circular polarization deteriorates fairly rapidly as soon as one deviates from the principal direction of the beam. This poses a problem, for example, for a source antenna used for the illumination of a parabola or a lens.
The object of the invention is to propose a device for receiving and/or transmitting signals comprising a printed antenna of high quality of circular or linear polarization over a widened frequency band and over a wide angle sector.
Thus, the subject of the present invention is a device for transmitting and/or receiving electromagnetic waves comprising at least one radiating element for radiating a circular or linear polarization of given sense, characterized in that it comprises at least one means dimensioned and positioned with respect to the radiating element in such a way as to radiate, at the frequency of the radiating element, a circular or linear polarization of opposite sense to that of the radiating element and whose phase is adjusted so as to compensate for the cross component of the radiating element.